One well-known type of ultrasound imaging system, which is available commercially from numerous sources including the assignee hereof, is the static B-scan system. These typically involve a multiple segment (e.g. three) articulated arm, with a transducer attached at the end. The angular positions of the respective segments are monitored and encoded, typically by potentiometer means at the respective joints, whereby there is always available precise positional information concerning the transducer, and hence the portion of the patient being examined. Through mechanical manipulation of the transducer, images of high line density over a large field of view can be generated. Typically, these static images provide hard copy records of the highest image quality available in the ultrasound modality. Static scanning systems also involve disadvantages, however, arising partly from the limiting and cumbersome nature of the articulated arm. That is, the arm often hampers scanning in difficult apertures of the body, and complicates the initial surveying process to locate small lesions or to follow vascular structures. Additionally, the static nature of this display prevents the monitoring of organs in motion, due to respiration, heart action, or the like.
Another class of commercially available imaging system is the real-time variety, typically a sector or a near rectangular segment of a sector. These systems typically utilize small hand-held probes, which allow the user to survey the anatomy, and to follow vascular structures and to observe organs in motion. These systems often involve disadvantages as well, however, chiefly due to the limited field of view, the low line density in the image, and the lack of positional information repeatably to coordinate the viewing of an image with some fixed datum position. These advantages aggregate when there is a need to obtain a high quality hard copy record of the examination, in that the image quality itself often is a limitation, and in any event there is little or no positional information available to determine the precise location from which the hard copy record was obtained.
Recently, systems have been introduced which include dual functions, employing a real-time sector scanning aspect, as well as a static B-scan probe. One such system has been marketed since approximately November 1979 by Rohe Scientific Corporation of Santa Ana, California under the trade designation Model 7000 Static B-Scanning System. The Rohe system employs two discrete and distinct probes, one for conducting a real-time sector scan and the other for a static B-scan. Preferred techniques for use entail utilization of the real-time sector scanning unit for surveying and coarse examination purposes, followed by use of the static B-scan for detailed evaluation and hard copy production with respect to any lesions or the like first located utilizing the hand-held sector probe. The Rohe system therefore entails most of the disadvantages attendant to utilization of separate sector scan and B-scan systems. First, utilization of the sector-scan image for hard copy is somewhat deficient with respect to image quality, and perhaps more seriously lacks positional information which indicates precisely the plane on which the image was observed. Secondly, assuming that the static B-scan aspect is to be utilized for detailed examination and recording of a hard copy, it may well be difficult to relocate a lesion first encountered utilizing the sector scan head; in any event, extensive readjustment of transducer dependent controls is required prior to shifting from one mode to the other. That is, it will be apparent that utilization of transducers of separate, distinct character for static B-scan and real-time sector scan applications, require different functional and signal processing constraints throughout the imaging system, with respect to timing, level selection, and the like.
It is a primary object of the present invention to provide an ultrasound imaging system which combines the beneficial attributes of static B-scan and real-time sector scan systems, by combining those functions in a manner which substantially eliminates their respective disadvantages.
It is a related object to provide a combined static B-scan and real-time sector scan system, utilizing a single transducer mechanism for both functions, whereby the user is free to shift operation back and forth between the respective modes, thereby vastly to increase the utility of the system. It is an associated object that such shifting back and forth may be accomplished free of the need for extensive readjustment or recalibration.
It is yet another object of the principles of the present invention to provide a combined system whereby positional information is available even when images are being developed, and, as desired, recorded, utilizing the real-time scan mode.
In a concurrently filed copending application of C. Hottinger entitled "ULTRASONIC IMAGING SYSTEM EMPLOYING REAL-TIME MECHANICAL SECTOR SCANNER", U.S. Ser. No. 178,482, which is assigned to the assignee hereof, there is disclosed and claimed a class of real-time sector scanners particularly useful in accordance with the principles of the present invention. The Hottinger system sets forth a form of real-time mechanical sector scanner wherein a positionally fixed, focusing transducer emits and receives ultrasound energy along an axis, and an oppositely facing sonic reflector or mirror is pivoted about a fulcrum on the axis, to reflect sonic energy between the transducer and the subject. Thus, beams between the reflection face and the subject lie in a different spatial plane than do beams between the transducer and the subject. In addition to setting forth the basic premise of such operation, the Hottinger application discloses respective embodiments wherein the mirror is located intermediate the transducer and the source of oscillatory motive power, and wherein the mirror is located "outboard" of the transducer relative to the source of oscillatory motive power.
Another concurrently filed, copending application assigned to the assignee hereof, of J. Sorwick entitled "MECHANICAL SECTOR SCANNER HEAD AND POWER TRAIN", U.S. Ser. No. 178,488, sets forth a preferred design for sector scanning heads employing the rationale set forth in the Hottinger application. In accordance with the teachings of the Sorwick application, a preferred arrangement locates the transducer on the side of the oscillating mirror opposite the source of oscillatory power. A curved faced, disc-shaped transducer and an oppositely facing, circular angularly disposed mirror form the transmission and reception path of a mechanical sector scan imaging system. The transducer and mirror are mounted on a common axis, where the fulcrum for mirror movement also is located. A shaft upon which the mirror is affixed oscillates about the same axis, and through a belt drive mechanism, a spacially eccentric motor provides the oscillating motion to the mirror, in turn scanning ultrasound beams through the subject by virtue of mirror motion. Hence, the Sorwick application describes a configuration which is extremely compact and convenient to use for real-time scanning applications, allowing the user readily to follow patterns of vascularization, to image body portions which are in motion due to respiratory, cardiac, or the like movements, and to have access to difficult to reach portions of the body.
It is an object of the present invention to utilize real-time sector scan apparatus and principles, as taught by the previously referenced Hottinger and Sorwick concurrently filed applications, in conjunction with static B-scan arms and systems, to achieve an efficient, mutually compatible combined system which meets the foregoing objects of the present invention.